At SFDC we bought and used internally a tool called Rypple (later work.com) that was precisely that.
As you say, zero impact to people in terms of their performance reviews (which were a topic of discussion in their own, each employee having to write a mini-manifesto for their year ahead) and kinda became a popularity contest where people were giving kudos to their office buddies.
And don't get me started on the people that left heart stickers with messages like "thank you for starting the best company in the world" on Benioff's profile.
Hah, similar thing happened for me. I think the main issue was that departments that relied on creative problem-solving (e.g. business development) ended up being way louder than others that didn't as much (e.g. QA)
Another issue is that tech orgs are extremely political. There was one person who had single-handedly created a viable migration path from the company's aging proprietary framework to .NET MVC5, but no kudos there. Just lots of pushback and skepticism.
As you say, zero impact to people in terms of their performance reviews (which were a topic of discussion in their own, each employee having to write a mini-manifesto for their year ahead) and kinda became a popularity contest where people were giving kudos to their office buddies.
And don't get me started on the people that left heart stickers with messages like "thank you for starting the best company in the world" on Benioff's profile.